As examples of feedback control, proportional control and integral control are known. With the proportional control, a deviation between an indicating value input from the outside and a feedback value output from a controlled object in accordance with this indicating value decreases. The proportional control however has a limitation with regard to diminishing this deviation.
Meanwhile, with the integral control, the aforementioned deviation which is difficult to diminish with the proportional control can be further reduced. An manipulated variable input to the controlled object however can go above and below the indicating value in performing the integral control.